In some electric power distribution systems, a main-tie-tie-main configuration is used. In accordance with a main-tie-tie-main configuration, a first load bus powered via a first main breaker and a second load bus powered via a second main breaker can be connected together by closing two bus tie breakers that are connected between the two load busses. The first load bus can be powered by the same power source as the second load bus or by a different power source. For example, the first load bus may be connected to a static transfer switch that can selectively deliver power to the first load bus from a first power source or a second power source while the second load bus may simply be powered by the first power source.
In such an arrangement, it may be deemed necessary or desirable to take the static transfer switch offline (e.g., for maintenance) while still providing power to the first load bus. To achieve this, the first load bus may be disconnected from the static transfer switch and connected to the second load bus by closing the bus tie breakers, after which the first load bus is powered via its connection to the second load bus. To ensure continuity of power to the loads connected to the first load bus, a closed-transition or make-before-break transfer procedure may be used to perform this operation. In accordance with such a procedure, the static transfer switch remains connected and supplies power to the first load bus until the second load bus is also connected to the first load bus via the closing of one or more of the bus tie breakers. After this, the static transfer switch is disconnected from the first load bus. To carry out the closed-transition procedure safely, it is critical to ensure that the first load bus and the second load bus are both being powered by the same power source before the bus tie breakers are closed.